Hitherto, there have been proposed a variety of block copolymers each formed of polymer blocks (A) predominantly containing aromatic vinyl compound units and polymer blocks (B) predominantly formed of conjugated diene compound units, which are called “A-(B-A)n” type block copolymers or “(A-B)n” type (wherein n is an integer of 1 or more) block copolymers, as well as corresponding hydrogenated block copolymers produced by hydrogenating carbon-carbon double bonds originating from the conjugated diene compound units forming the polymer blocks B. By virtue of excellent flexibility and mechanical properties, the hydrogenated block copolymers have been conventionally used as an alternative to vulcanized rubber and soft vinyl chloride for production of various articles.
Meanwhile, many articles, including home appliances, electronic parts, machine parts, and automobile parts are produced from a wide variety of polar resins, resins containing an inorganic filler (particularly, glass fiber), ceramic materials, glass materials, and metals, which are excellent in durability, heat resistance, and mechanical strength. In some cases, a highly flexible elastomer member is attached to or hybridized with these articles for the purposes of fixation to other structural members, shock absorption, prevention of breakage, sealing, etc., depending on the use, configuration, application mode, etc. of the articles.
Such elastomer members would be formed from a thermoplastic elastomer composition comprising the aforementioned hydrogenated block copolymer which is a suitable material having excellent flexibility, mechanical properties, and moldability. However, since the hydrogenated block copolymer is a material of low polarity, the block copolymer has insufficient adhesion to polar resin, resin containing inorganic filler (particularly, glass fiber), ceramic material, glass, metal, etc. Without any further treatment, the block copolymer is difficult to adhere to such a material through melt adhesion, which is problematic. Therefore, in order to adhere the hydrogenated block copolymer to polar resin, resin containing inorganic filler (particularly, glass fiber), ceramic material, glass, or metal, an adhesive is used, or the surface of polar resin, resin containing inorganic filler (particularly, glass fiber), ceramic material, glass, or metal is treated in advance with a primer or the like (see Patent Documents 1 to 6).
However, the aforementioned method employing an adhesive or a primer makes the production steps cumbersome, to thereby lower productivity and elevate production cost. For dissolving such problems, Patent Document 7 discloses a thermoplastic polymer composition comprising the block copolymer and polyvinyl acetal, the composition providing excellent adhesion to polar resin, glass, metal, or ceramic material. Patent Document 7 also discloses that use of the block copolymer in combination with a similar block copolymer having a polar functional group leads to enhancement in mechanical properties and adhesion, with preventing an increase in material cost. These physical properties are considered to be enhanced through the following mechanism. That is, the block copolymer having a polar functional group enhances the compatibility of the block copolymer to polyvinyl acetal, whereby dispersibility of the polyvinyl acetal phase increases, and the interfacial adhesion of the block copolymer phase is reinforced. However, the thermoplastic polymer composition containing, in combination, the block copolymer and a similar block copolymer having a polar functional group tends to exhibit high melt viscosity, although it exhibits excellent flexibility, mechanical properties, and adhesion. Thus, when the thermoplastic polymer composition is subjected to injection molding or a similar working process, fluidity of the composition must be further improved. In addition, due to low fluidity, the thermoplastic polymer composition must be molded at high temperature. Since the composition may generate strong shear or heat during molding, the article tends to be deteriorated or to be colored. In addition, the flexibility, mechanical properties, moldability, and coloring resistance of the thermoplastic polymer composition disclosed in Patent Document 7 may be further enhanced. Previous studies by the present inventors have revealed that in some cases the adhesion provided by the composition is not necessarily excellent.